Remove tox-py35-on-zuul from zuul-jobs

We now have some real usage of tox on this repo itself, so the
self-testing of the tox environment we got from running this job
is now supplied by that.  The tox-py35-on-zuul job takes a while
to run and is sometimes flaky, so remove it so that it doesn't
act as an unecessary blocker.

Change-Id: Ifc274f049381cacead030e4baac460a7697c20cc

zuul.d/projects.yaml

@@ -1730,7 +1730,6 @@
         - openstack-infra-multinode-integration-opensuse423
         - openstack-zuul-jobs-linters
         - tox-py27
-        - tox-py35-on-zuul
         - tox-py35
     gate:
       jobs:
@@ -1750,7 +1749,6 @@
         - openstack-infra-multinode-integration-opensuse423
         - openstack-zuul-jobs-linters
         - tox-py27
-        - tox-py35-on-zuul
         - tox-py35
     post:
       jobs: